In underground irrigation or sprinkler systems, particularly those used for watering lawns, water distribution lines are used to carry water from a main supply line to various parts of the area to be watered, and sprinkler heads are connected to the water distribution lines at selected points. The cost of labor for the installation of a sprinkler system is generally the largest portion of the total cost, so it is advantageous for designers and installers of sprinkler systems to utilize designs and components that will minimize the time required for installation. In terms of material cost, modern sprinkler system design utilizes inexpensive plastic piping (constructed of PVC or other suitable materials) for the water distribution lines, and those lines are usually the least costly element. The sprinkler heads are typically the most costly material item, although the cost of the coupling devices installed between the water distribution lines and the sprinkler heads can also be significant. It is advantageous, therefore, to design sprinkler systems to minimize material costs as well as labor costs.
In typical practice, the water distribution lines are buried at a single selected elevation and the connection between each sprinkler head and the distribution line is made with a "swing arm" that includes a number of elbows and joints to allow adjustment of the elevation of the sprinkler head relative to the distribution line. Although water distribution lines should be placed below the "freeze depth" in the soil, the lines are most commonly buried substantially deeper than required for freeze protection, especially in mild climates. The swing arms in common use are designed to allow an installer to manipulate the swing arm to adjust the sprinkler head elevation relative to the water distribution line, and include several elbows and connecting conduits for that purpose. An example may be found in U.S. Pat. No. 5,458,290 to Johnson (e.g., element 40 of FIG. 3). Such swing arms require relatively large excavations at each sprinkler head location, with relatively high installation cost. The use of a number of elbows, conduits, etc. in the swing arms not only increases the cost of the components and/or installation, but also results in significant pressure drop through the swing arm. Since most sprinkler systems include a substantial number of sprinkler heads, the cumulative effect of the pressure loss through the swing arms can be significant.
The use of swivel couplings to facilitate installation of swing arms is known in the art, but the swivel couplings disclosed by the prior art typically require the use of O-rings or more complex sealing arrangements, are relatively complex in structure, and require specially formed components. Examples of swivel coupling designs known in the prior art may be found in U.S. Pat. No. 4,998,755 to Reader, and in U.S. Pat. No. 5,040,729 to Carrozza.
The use of barbed fittings in a swing arm is disclosed by U.S. Pat. No. 5,242,112 to Dunn, et al. This approach does reduce the complexity of the joints in the swing arm, but connections made with barbed fittings are prone to leakage problems and can be relatively easily dislodged if the connected sprinkler head is disturbed by, for example, the impact of a mower. The swing arm designs known in the prior art also have little, if any, flexibility other than through movement of the joints, so they do not readily accommodate forces imposed by the impact of an object, such as a mower, against a sprinkler head attached to the swing arm.
Flexible risers or nipples are also known in the prior art, as exemplified by U.S. Pat. No. 4,314,717 to Bjurman, and can be used to provide a flexible extension for mounting a sprinkler head. While flexible risers can be effective in reducing the probability of damage to a sprinkler head, they do not alone provide a comprehensive coupling system that meets the need for economy, ease of installation, and effective protection.
There remains an unfilled need for a flexible swivel coupling for use in sprinkler systems, and particularly for the mounting of sprinkler heads, that is economical to produce, that facilitates design and installation of sprinkler systems so as to reduce the cost of both materials and labor, that provides effective protection against damage to sprinkler heads, and that facilitates the performance of necessary maintenance and repairs.